The present invention relates generally to an automatic transmission comprising a ratio-change mechanism, which transmits the rotational driving force of a drive power source varying a speed ratio, and a forward/reverse direction-change mechanism, which changes the direction of the rotation of the driving force. Furthermore, the present invention relates to an automatic transmission that comprises a belt-type continuously variable speed control mechanism as ratio-change mechanism.
Such an automatic transmission is designed for use in a vehicle to transmit the rotational driving force of an engine (drive power source) varying a speed ratio, in which the rotational speed being transmitted is controlled in correspondence to the throttle opening of the engine, the speed of the vehicle, etc. Such an automatic transmission generally comprises hydraulic actuators such as hydraulic clutches and brakes to achieve this speed ratio control. For example, an automatic transmission may comprise a belt-type continuously variable speed control mechanism disclosed in Japanese Laid-Open Patent Publication No. H08(1996)-178059. In this case, the automatic transmission comprises a clutch mechanism that transmits the driving force of the engine to the transmission, in addition to the belt-type continuously variable speed control mechanism, and these mechanisms are controlled by supplies of hydraulic pressure. While the shift lever is at xe2x80x9cNxe2x80x9d position, the clutch mechanism is released to set the transmission in neutral condition. When the shift lever is shifted from xe2x80x9cNxe2x80x9d position to xe2x80x9cDxe2x80x9d position, the clutch mechanism is engaged, and the continuously variable speed control mechanism is set in speed ratio control. In this instance, if the clutch mechanism is brought into engagement abruptly, then a shock may happen. To avoid such a shock, the hydraulic pressure supplied to the clutch mechanism is gradually increased by means of a solenoid valve.
By the way, another construction of automatic transmission is known, which transmission comprises a forward/reverse direction-change mechanism provided on the output side of the engine, a belt-type continuously variable speed control mechanism provided in connection to the forward/reverse direction-change mechanism, and a starting clutch mechanism connected to the output shaft of this continuously variable speed control mechanism. In this case, the starting clutch mechanism is used for controlling the power transmission to the drive wheels. When the shift lever is at xe2x80x9cNxe2x80x9d position (neutral range), the transmission is set in neutral condition. In this condition, the starting clutch mechanism is in disengagement, so the power transmission through the starting clutch mechanism is cut off. In addition, the forward/reverse direction-change mechanism is also disengaged in this condition.
In this automatic transmission, when the shift lever is shifted from xe2x80x9cNxe2x80x9d position to xe2x80x9cDxe2x80x9d position (for the forward drive range), the line pressure is led to the forward drive clutch that actuates the forward/reverse direction-change mechanism into engagement. At the same time, a pressure for starting control is supplied to the starting clutch to actuate it into engagement. In this way, the rotational direction of the driving force of the engine is set by the forward/reverse direction-change mechanism, the rotational speed to be transmitted is determined by the continuously variable speed control mechanism in speed ratio control, and the transmission of this rotation to the drive wheels is controlled by the starting clutch. Especially, the starting clutch is controlled appropriately to start the vehicle smoothly.
In this automatic transmission, however, as the pulleys comprising the continuously variable speed control mechanism have a relatively large inertia, when the forward/reverse direction-change mechanism is brought into engagement by the supply of the line pressure, the continuously variable transmission having a large inertia is connected to the output shaft of the engine. As a result, even though the starting clutch is disengaged, the whole of the power plant including the engine experiences a vibration as the engine tries to rotate the transmission against the large rotational inertia. This vibration is transmitted to the body of the vehicle, which supports the power plant, and induces a shaking of the vehicle body. As the rotational speed of the engine is reduced temporarily, a rotational vibration or a noise may also occur. These same problems may be also experienced when the shift lever is shifted from xe2x80x9cNxe2x80x9d position to xe2x80x9cRxe2x80x9d position (for the rearward drive range) or when the shift lever is shifted directly from xe2x80x9cDxe2x80x9d position to xe2x80x9cRxe2x80x9d position or from xe2x80x9cRxe2x80x9d position to xe2x80x9cDxe2x80x9d position.
It is an object of the present invention to provide a control system for an automatic transmission, which system can bring the forward/reverse direction-change mechanism into engagement smoothly, preventing any vibration or noise that may otherwise occur when the shift lever is operated in the above described ways.
According to the present invention, an automatic transmission comprises a ratio-change mechanism (for example, the metal V-belt mechanism 10 described in the following embodiment, another type of continuously variable transmission, a normal transmission, etc.), a forward/reverse direction-change mechanism (for example, the forward/reverse direction-change mechanism 20 described in the following embodiment, another type of forward/reverse direction-change mechanism, etc.) and a forward/reverse direction-change actuator (for example, the forward clutch 30 and the reverse brake 25 described in the following embodiment). The ratio-change mechanism transmits rotational driving force from a drive power source (for example, the engine ENG in the following embodiment) changing a speed ratio, and the forward/reverse direction-change mechanism switches the rotational direction of the rotational driving force transmitted from the drive power source through the ratio-change mechanism. The forward/reverse direction-change actuator, by receiving a hydraulic pressure, actuates the rotational direction switching operation of the forward/reverse direction-change mechanism. A control system for this automatic transmission comprises a regulator valve (for example, the regulator valve 50 described in the following embodiment), a manual switching valve (for example, the manual valve 80 described in the following embodiment) and a switching operation detector (for example, the drive-range sensor 105 described in the following embodiment). The regulator valve generates a line pressure by adjusting the pressure of a hydraulic pressure source, the manual switching valve is operated by an external factor, to switch the supply of oil at the line pressure to the forward/reverse direction-change actuator, and the switching operation detector detects the movement of the manual switching valve. When the movement of the manual switching valve to a position where the line pressure is to be supplied to the forward/reverse direction-change actuator is detected by the switching operation detector, the line pressure, which is adjusted by the regulator valve, is lowered for a predetermined time period immediately after this detection.
With this control system, for example, when the shift lever is manipulated from xe2x80x9cNxe2x80x9d position to xe2x80x9cDxe2x80x9d position to shift the manual switching valve from its N position to its D position, the line pressure adjusted by the regulator valve is supplied to the forward clutch (or to the reverse brake), which constitutes the forward/reverse direction-change mechanism, for the engagement of the forward clutch. In this instance, during the predetermined time period after the manual switching valve has set at the D position, the line pressure, which is adjusted by the regulator valve, is lowered to gradually engage the forward clutch. In this way, the ratio-change mechanism, which has a relatively large rotational inertia, is brought gradually into engagement with the output shaft of the engine. As the rotational inertia of the ratio-change mechanism is gradually received by the output shaft of the engine, the forward clutch is smoothly brought into engagement without any shock or noise.
This automatic transmission may comprise a ratio-controlling actuator (for example, the drive cylinder chamber 14 and the driven cylinder chamber 19 described in the following embodiment), which receives a hydraulic pressure to actuate the speed ratio control of the ratio-change mechanism. In this case, the ratio-controlling actuator receives the line pressure to actuate the speed ratio control. The hydraulic pressure supplied to this ratio-controlling actuator is to control the torque transmission of the ratio-change mechanism. When the line pressure supplied to the forward clutch is low, the torque transmission through the forward clutch is small. Therefore, there is no problem to supply this low line pressure also to the ratio-controlling actuator. By lowering the line pressure in this way, the power requirement for running the pump to generate the line pressure is reduced to improve fuel efficiency.
According to another feature of the present invention, an automatic transmission comprises a continuously variable speed control mechanism (for example, the metal V-belt mechanism 10 described in the following embodiment), a forward/reverse direction-change mechanism (for example, the forward/reverse direction change mechanism 20 described in the following embodiment) and a forward/reverse direction-change actuator (for example, the forward clutch 30 and the reverse brake 25 described in the following embodiment). In this case, the continuously variable speed control mechanism comprises a variable width drive pulley, a variable width driven pulley and belt means, which is disposed around these pulleys, for transmitting the rotational driving force of a drive power source (for example, the engine ENG in the following embodiment) at a continuously variable speed change ratio. The forward/reverse direction-change mechanism switches the rotational direction of the rotational driving force transmitted from the drive power source through the speed control mechanism, and the forward/reverse direction-change actuator, by receiving a hydraulic pressure, actuates the rotational direction switching operation of the forward/reverse direction-change mechanism. A control system for this automatic transmission comprises a regulator valve (for example, the regulator valve 50 described in the following embodiment), a manual switching valve (for example, the manual valve 80 described in the following embodiment) and a switching operation detector (for example, the drive-range sensor 105 described in the following embodiment). The regulator valve generates a line pressure by adjusting the pressure of a hydraulic pressure source, the manual switching valve is operated by an external factor, to switch the supply of oil at the line pressure to the forward/reverse direction-change actuator, and the switching operation detector detects the movement of the manual switching valve. When the movement of the manual switching valve to a position where the line pressure is to be supplied to the forward/reverse direction-change actuator is detected by the switching operation detector, the line pressure, which is adjusted by the regulator valve, is lowered for a predetermined time period immediately after this detection.
In this arrangement, also, when the shift lever is manipulated from xe2x80x9cNxe2x80x9d position to xe2x80x9cDxe2x80x9d position to engage the forward clutch, during the predetermined time period after the manual switching valve has set at the D position, the line pressure, which is adjusted by the regulator valve, is lowered to gradually engage the forward clutch. In this way, the continuously variable speed control mechanism, which has a relatively large rotational inertia, is brought gradually into engagement with the output shaft of the engine. As the rotational inertia of the continuously variable speed control mechanism is gradually received by the output shaft of the engine, the forward clutch is smoothly brought into engagement without any shock or noise.
Furthermore, the control system may comprise a drive cylinder chamber provided in the drive pulley, a driven cylinder chamber provided in the driven pulley and a shift control valve (for example, the drive and driven shift control valves 60 and 65 described in the following embodiment), which controls a supply of hydraulic pressure to the drive cylinder chamber and the driven cylinder chamber. In this case, the shift control valve controls the supply of oil at the line pressure to the drive cylinder chamber and the driven cylinder chamber. With this arrangement, when the line pressure is lowered during the predetermined time period after the manual switching valve has shifted to the position where the line pressure is to be supplied to the forward/reverse direction-change actuator, the drive and driven cylinder chambers also receive this lowered line pressure. Because of the line pressure being lowered in this way, the power requirement for running the pump to generate the line pressure is reduced to improve fuel efficiency.
The forward/reverse direction-change mechanism may be disposed between the drive power source and the continuously variable speed control mechanism, and clutching means (for example, the starting clutch 40 described in the following embodiment) for controlling the transmission of the drive power may be provided on the output side of the continuously variable speed control mechanism. In this case, the lowered line pressure is used for engaging the forward/reverse direction-change mechanism smoothly and then for engaging the clutching means smoothly, thus achieving a smooth starting operation.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.